Given the opportunity to send a text message to a tree, it's difficult to know what to say. Nothing too personal, nothing that may cause offence and nothing that requires a reply. But the novelty of saving a number under the name Tree in my phone book and the temptation of the message on the small LED screen strapped to its trunk, saying TEXT ME ON 07743 100 749, is too much to resist. I immediately text an excited: ''Hello tree!''

Eight trees in Loch Lomond & The Trossachs National Park have been given their own mobile phone numbers as part of a series of six artworks newly launched to celebrate and record the park's designation. The 4 Luv project, by Siobhan Hapaska and Fiddian Warman, is a text messaging network on a trail at Balmaha on the eastern side of the Loch, at Firkin Point on the west side and by the Gateway Centre at Loch Lomond Shores, Balloch.

''The key idea was to bring together the notion of people carving messages into trees with the current practice of using sms messages for flirting,'' says Fiddian. Instead of engraving ''Dave 4 Eva'' into bark and harming the tree, then, exclamations of love can be texted.

Romance may have been the inspiration, but Fiddian is happy for the service to be used for other ends. ''I'd like it to be very open,'' he says. ''I hope people find their own uses for it.'' He has only sent a ''boring'' test message so far, but intends to send more through the project's website, www.4Luv.org, where messages will be stored on a database to create a history of the tree's community.

This collision of nature and technology is not accidental. During Fiddian and Siobhan's research, they paid particular attention to the industrial history of Loch Lomond and its proximity to Glasgow and how this apparently contradicts its perceived wildness. ''We wanted to do something that played on the notions of city and country and natural and unnatural,'' says Fiddian. ''That's implicit in the piece.''

As environmental art projects go, the Loch Lomond one is ambitious. Other pieces include a bird habitat with berry-like football feeders and television aerial perches by Mary Redmond and a sculpture which holds seven LCD video screens showing seven waterfalls which feed into the Loch by Donald Urquhart. The park worked with arts commission organisation The Centre, with initial commissioning done by Lucy Byatt and the latter stages of the

project overseen by Jenny Cowie.

''At one point, it was going to be along the lines of carved animals, but it was decided that it would be much more interesting to commission artists,'' says Jenny. ''It isn't about focusing on that kind of craft aesthetic with materials, the focus here is on ideas. A lot of artists were looked at and it was an ongoing process of the park understanding what the artists were doing and how they could respond to the site.''

The result is a collection which suggests a slightly academic, highly personal relationship to the land, rather than naturalistic. ''It's about the artists' individual responses to the park,'' says Jenny. ''They've personally responded to the overall aims of the park, about conservancy and the economic push behind it. They've all responded very differently. Olaf is very much a cool take on the land management issue, while Mary's is much more about her personal ideas about viewing animals.''

Although the art is challenging, the layout is more conventional. ''We'd hoped to avoid the sculpture trail route and I don't think we have,'' says Jenny. ''It is a sculpture trail in a sense, although the pieces are not what you would traditionally perceive as sculpture. They're a broad church. In the context of other environmental art projects, Grizedale Sculpture Park, for example, is an ongoing series of temporal projects in the forest, more like a gallery space but outdoors. Here, it's much more contained and the works will be here for 15 years.''

Indeed, you don't have to travel far to see another different approach to environmental art. The three-year Galloway Forest Art Programme features commissions from seven artists and craft makers, which are hidden along various routes and tracks. It is intended that walkers, cyclists, anglers and people driving through the park discover and interpret the pieces.

Tom Littlewood, public art officer for Dumfries & Galloway Art Association, managed the project. ''When we commissioned there was a conscious effort to get away from people being conditioned to go and see art in the gallery context,'' he says. ''We wanted to develop a sense of place within the forest context. All the works are accessible and all are open to the public, but you need to make an effort to see them. There's little signage. It's quiet, but in doing that people have come to know them.''

Unlike the Loch Lomond project, there's deliberate stress on craft, not concept. Quorum by Matt Baker is a series of carved stone heads built into an existing sheep fold, near Black Loch off the Queensway. The Eye by Colin Rose is an eight-metre-high spire constructed from red-earth tiles, also by Black Loch.

''If it's conceptual work that doesn't speak for itself within the landscape then that's not a sound approach,'' says Tom.

Over the years, the pieces will become more of a part of that landscape. They will, Tom says, ''grow old gracefully''. True to form, The Eye is beginning to moss and The Otter by Gillian Ford, carved from granite, is showing the gloss of being patted and sat on. Some of the more temporal works have gone the way of nature, while others have become fully integrated with the people and places within the park. Colin Rose would perhaps prefer his imposing red spire to be called by its given name, but it's surely a mark of the project's success that locals have nicknamed it The Carrot.

As far as my own relationship with art goes, I'm still waiting for a return greeting from that tree I texted at Loch Lomond.